# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
# Copyright(C) 2013-2018 Max-Planck-Society
#
# NIFTy is being developed at the Max-Planck-Institut fuer Astrophysik
# and financially supported by the Studienstiftung des deutschen Volkes.

from .iteration_controller import IterationController
from ..logger import logger


class GradientNormController(IterationController):
    """An iteration controller checking (mainly) the L2 gradient norm.

    Parameters
    ----------
    tol_abs_gradnorm : float, optional
        If the L2 norm of the energy gradient is below this value, the
        convergence counter will be increased in this iteration.
    tol_rel_gradnorm : float, optional
        If the L2 norm of the energy gradient divided by its initial L2 norm
        is below this value, the convergence counter will be increased in this
        iteration.
    convergence_level : int, default=1
        The number which the convergence counter must reach before the
        iteration is considered to be converged
    iteration_limit : int, optional
        The maximum number of iterations that will be carried out.
    name : str, optional
        if supplied, this string and some diagnostic information will be
        printed after every iteration
    """

    def __init__(self, tol_abs_gradnorm=None, tol_rel_gradnorm=None,
                 convergence_level=1, iteration_limit=None, name=None):
        super(GradientNormController, self).__init__()
        self._tol_abs_gradnorm = tol_abs_gradnorm
        self._tol_rel_gradnorm = tol_rel_gradnorm
        self._convergence_level = convergence_level
        self._iteration_limit = iteration_limit
        self._name = name

    def start(self, energy):
        """ Start a new iteration.

        The iteration and convergence counters are set to 0.

        Parameters
        ----------
        energy : Energy
            The energy functional to be minimized.

        Returns
        -------
        int : iteration status
            can be CONVERGED or CONTINUE
        """
        self._itcount = -1
        self._ccount = 0
        if self._tol_rel_gradnorm is not None:
            self._tol_rel_gradnorm_now = self._tol_rel_gradnorm \
                                       * energy.gradient_norm
        return self.check(energy)

    def check(self, energy):
        """ Check for convergence.

        - Increase the iteration counter by 1.
        - If any of the convergence criteria are fulfilled, increase the
          convergence counter by 1; else decrease it by 1 (but not below 0).
        - If the convergence counter exceeds the convergence level, return
          CONVERGED.
        - If the iteration counter exceeds the iteration limit, return
          CONVERGED.
        - Otherwise return CONTINUE.

        Parameters
        ----------
        energy : Energy
            The current solution estimate

        Returns
        -------
        int : iteration status
            can be CONVERGED or CONTINUE
        """
        self._itcount += 1

        inclvl = False
        if self._tol_abs_gradnorm is not None:
            if energy.gradient_norm <= self._tol_abs_gradnorm:
                inclvl = True
        if self._tol_rel_gradnorm is not None:
            if energy.gradient_norm <= self._tol_rel_gradnorm_now:
                inclvl = True
        if inclvl:
            self._ccount += 1
        else:
            self._ccount = max(0, self._ccount-1)

        # report
        if self._name is not None:
            msg = self._name+":"
            msg += " Iteration #" + str(self._itcount)
            msg += " energy={:.6E}".format(energy.value)
            msg += " gradnorm={:.2E}".format(energy.gradient_norm)
            msg += " clvl=" + str(self._ccount)
            logger.info(msg)
            # self.logger.info(msg)

        # Are we done?
        if self._iteration_limit is not None:
            if self._itcount >= self._iteration_limit:
                logger.warning(
                    "Warning:Iteration limit reached. Assuming convergence")
                return self.CONVERGED
        if self._ccount >= self._convergence_level:
            return self.CONVERGED

        return self.CONTINUE